1. Field Of The Invention
This invention relates to a diesel pile driving hammer, and more particularly, a diesel pile driving hammer provided with interchangeable rams.
2. Description of the Prior Art
Diesel pile driving hammers are drop hammers. A ram within an outer cylindrical casing is used to contact an anvil connected to a drive cap seated on the pile. The initial power to lift the ram is furnished by a hoist line carrying the ram upward on a trip block. At the top of the start stroke, the ram is released from the hoist line to fall through the outer hammer cylinder casing and to successively close the cylinder casing intake-air exhaust openings, compress and heat entrapped air which has been captured within the cylinder casing between the ram and anvil and explode atomized diesel fuel which has been injected and mixed with the entrapped and compressed air. The explosion of the fuel mixture of entrapped air and injected diesel fuel sends the ram back up the cylinder casing, exhausting the spent gases, and commencing a repeat of the cycle. The hammer is stopped by interrupting the fuel flow into the cylinder casing. During the dropping of the ram, the ram will contact the anvil to drive the pile and drive cap as it compresses the fuel mixture, just prior to the explosion which drives the ram back up to the top of its stroke wherein the cycle is repeated.
Standard diesel hammers have ram weights varying from one thousand to twenty thousand pounds. The theoretical available impact energy delivered per blow by a diesel hammer is a function of the the amount of fuel introduced into the hammer, the ram weight, and the efficiency of combustion within the cylinder. Traditional means of designing impact atomization diesel pile hammers to provide different delivered impact energy values has been to vary the ram weight and the fuel volume introduced into the hammer cylinder. The flight of the ram is the indicator of the efficiency of the explosive force at impact, since about all of the net energy from the exploding fuel is utilized in propelling the ram upward. The net energy of the explosion is thus reflected by the ram stroke times the ram weight. Accordingly, to obtain maximum impact it is necessary to maintain the proportional geometry of the combustion chamber, e.g., to obtain the optimum efficient fuel mixture volume, so that the maximum upward flight of the ram is obtained upon the utilization of different ram weights. This has been accomplished in the past by providing different cylinder shell or casing sizes with rams of different weights.
Relatively recently, the user of pile drive hammers, the foundation contractor, has been charged with not only providing a specific delivered energy from a hammer used to install pile foundations, but also to provide a hammer with its ram weight restricted within a range for a specific energy output and pile to be driven. Accordingly, it has become more economical to design a pile driving hammer having a single cylindrical casing with interchangeable rams of different weights within the specified range and to maximize the geometry of the combustion chamber in the outer cylindrical casing so as to arrive at the required specific, delivered energy from the hammer per blow. Such a hammer also provides for considerable investment economy for the user in that all that is necessary are interchangeable, different weight rams interfacing with the same cylinder and anvil block. The rams used may be of different weight and the final compressed air volume and thus fuel mixture may be varied by reducing the height of the annulus formed between the bottom edge of the ram piston and the top edge of the anvil block at contact, by changing the ram and/or piston geometry. Additional control of the fuel mixture may also be accomplished at the fuel pump introducing atomized fuel into the combustion chamber and by reducing the swept volume of air compressed in the combustion chamber at ram-anvil contact, by providing auxiliary, alternate, air inlet-exhaust ports at a location lower than the normal air inlet-exhaust ports in the outer cylinder casing wall. These auxiliary ports can be closed with high strength pipe plugs when not needed, for example, when a ram of a lighter weight is used.
As indicated, one of the design problems in achieving the required impact energy per blow for a different ram of heavier weight in the same cylindrical casing has been to maintain the proper proportional geometry of the combustion chamber for a particular ram weight and thus fuel mixture so as to achieve the required flight of the ram during each stroke of its cycle. One attempted solution as noted above, was to provide auxiliary air inlet-exhaust ports to reduce the swept volume of air compressed in the combustion chamber. But, since the inlet ports of an impact diesel pile hammer are also the exhaust ports, the ports must also provide a sufficient nonrestricted opening to expel all of the exhaust gases of combustion in the time it takes the ram to travel its upward stroke, which may be on the order of less than 0.35 seconds, while also providing a reduction in the swept volume of air introduced into the combustion chamber.